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Appendix; PI Regulation
Example:
The set-point is 40%, and the min. speed is 50%.
1. Selecting a new set-point. Choose a value that will
raise the set-point about 10% higher than the min.
speed.
New set-point = % min. speed x 1.1 = 55%
2. Setting parameter 125. Apply the same increase to
this parameter. 100 x 1.1 = 110%
Parameter 201:
Set min. frequency if required.
If you enter a min. speed you must observe the following:
•
When min. speed is used parameter 411 must be set
to "proportional with min. limit".
•
If the min. frequency % is higher than the set-point %
you must re-scale parameter 125 and the set-point.
Parameter 202:
Max. frequency is normally set to 50 Hz. Running
centrifugal pumps and fans above this speed will cause
overload of the pump or fan, as the power increases to
the third power of the speed change.
Example:
If the speed increased to 60 Hz the power will increase
by a massive 173%.
Set at 50 Hz.
Parameter 205:
The internal set-point for the regulator.
Enter the set-point % value.
Externally it can be one of the choices of the analog
values. Use of one of the analog choices will prevent its
use as the feedback signal.
The use of the internal set-point reduces installation
costs. Up to 4 internal set-points (by using parameters
205-208) can be selected by a combination of 2 switches.
Refer to the instruction manual for further information.
The set-point can be found by calculating the percentage
of required signal from the transmitter range.
Example:
A pressure transmitter has range of 0-10 bar. A set-point
of 4 bar is required.
Set-point = 4/10 x 100 = 40%
Enter 40 in parameter 205.
Parameter 214:
Use only linear ramps.
Parameter 215 & 216:
The ramps only function on starting and stopping the
system.
Enter the ramp up and down times in seconds.
Parameter 315:
Set the motor thermal protection to trip 1 if thermal
protection of the motor is required.
Parameter 411:
This parameter must be changed from its default value
when PID regulation is used.
Set to "proportional with min. limit".
Parameter 412-413:
Set the type of analog input signal for the set-point
and feedback signals. Parameter 114 has previously set
up the selection of the feedback signal type.
If parameter 205 (internal set-point) is used either current
or voltage can be used as the feedback signal.
If one of the inputs is not used it must be set to no
operation.
Normal or Inverse Control
Introduction:
The control is called normal, if the motor speed is
increased when the feedback signal goes down, and the
motor speed is reduced if the feedback signal goes up.
Typical for pump pressure systems and air handling units
in variable air volume systems.
The control is called inverse if the motor speed is
increased when the feedback signal is increased. Typical
for pit pumping where: the faster the water flows into the
pit, the faster the pump must pump out the water.
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